The present invention is related to optical data storage media. More particularly, the present invention is related to limited play optical data storage media.
Optical, magnetic and magneto-optic media are primary sources of high performance storage technology, which enable high storage capacity coupled with a reasonable price per megabyte of data stored. The use of optical media has become widespread in audio, video, and computer data storage applications in such formats as compact disc (CD), digital versatile disc (DVD, including multi-layer structures like DVD-5, DVD-9 and multi-sided formats such as DVD-10, and DVD-18), magneto-optical disc (MO), and other write-once and re-writable formats such as CD-R, CD-RW, DVD-R, DVD-RW, DVD+RW, DVD-RAM, and the like, hereinafter collectively “data storage media”. In these formats, data are encoded onto a substrate into a digital data series. In pre-recorded optical media, such as CD, the data are typically pits and grooves embossed on the surface of a plastic substrate using a method such as injection molding, stamping or the like.
In recordable media, the data are encoded by laser, which illuminates an active data layer that undergoes a phase change, thus producing a series of highly reflecting or non-reflecting regions making up the data stream. In these formats, a laser beam first travels through a plastic substrate before reaching the data layer. At the data layer, the beam is either reflected or not, in accordance with the encoded data. The laser light then travels back through the plastic and into an optical detector system where the data are interpreted.
In some applications, it is desirable to limit the playable lifetime of an optical disc. For example, there is widespread interest in providing temporary access to music, movies, and other forms of digital entertainment without requiring a purchaser to return a data storage device to its provider. Put in very concrete terms, a customer purchasing a movie on a limited play DVD would be granted only limited access to the movie because by design, access to the data contained within the limited play DVD would be extinguished over a relatively short period of time after its first use. Another example is sample computer programs that are provided to potential customers in order to entice them to purchase the software. The programs are intended to be used for a limited period of time. In each of these applications and others, when that time has expired, the disc must be returned. Recycling concerns raised by such limited use schemes are balanced by the both recyclability of the limited play DVD itself and the elimination of at least one trip, typically in an automobile, to the site of the DVD's purchase.
Thus, a need exists for machine-readable optical discs which provide limited access to music, movies, other forms of digital entertainment, or any other data for which limited access is appropriate, wherein said optical discs do not need to be returned to the provider at the end of a limited period of access. Limited-play optical discs provide a solution to this problem.
Limited play discs such as DVD's have been produced by various methods. One method includes forming a disc comprising a reflective layer protected by a porous barrier layer such that the reflective layer becomes oxidized over a pre-determined period of time. Once the reflective layer attains a certain level of oxidation, the disc is no longer readable. Hence the time taken for the passage of oxygen through the substrate layer becomes very vital for the play-time of the limited play disks. Moreover, where the limited period of access is predicated on oxygen sensitivity of the DVD alone, steps must be taken such that the substrate possess the necessary level of oxygen permeability such that the oxygen does not reach the reactive layer before the pre-determined time, enabling the DVD remains fully playable during the limited period of access.
In view of the forgoing, there exists a need to protect the limited play data storage media from uncontrolled abridgement of the useful lifespan of the data storage media. The present invention provides novel solutions to these and allied problems as evidenced by the description, examples and claims that follow.